1. Field of the Invention
The present invention relates to a method of boosting the net engine torque of a variable displacement engine running in a variable displacement mode by using non-firing cylinders to boost manifold pressure.
2. Background Art
Vehicle engines including internal combustion engines and diesel engines are currently designed to maximize power while maximizing fuel efficiency and minimizing emissions.
xe2x80x9cCamlessxe2x80x9d engines (engines that do not have a conventional camshaft for actuating intake and exhaust valves) have been developed that, for example, would enable a four-stroke internal combustion engine to operate without a throttle to optimize engine operation. Camless engines may use hydraulic valve lifters or electromechanical valve lifters for actuating intake and exhaust valves.
A variable displacement engine (VDE) provided with camless valves permits one or more cylinders to be disabled under certain conditions to improve fuel economy. For example, a V8 camless VDE can be operated as a V4 during constant speed driving when the power requirement is low. When power requirements increase, the engine may be operated in a full cylinder mode with all cylinders firing.
One limitation of VDE engines is that when there is a large power demand, it is necessitated that it be shifted from the variable displacement mode to the full cylinder mode.
Another problem related to VDE engines is that the net engine torque available in the VDE mode limits the portion of the customer or regulatory driving cycle in which it may be utilized.
One attempt to address the above problems is disclosed in U.S. Pat. No. 4,671,226 to van Rinsum that discloses a supercharged multi-cylinder, four-cycle diesel engine which under partial loads has some cylinders operate as the engine while other cylinders operate as a compressor supplying compressed air to the firing cylinders. According to this patent, at least one additional valve must be provided for each cylinder head of the cylinders that are to be operated as a compressor. The additional valve is independent of the intake and exhaust valves. The additional valve controls an additional gas conduction channel that is connected to the intake or exhaust gas flow of the cylinders operating as a compressor. The extra valves and additional gas conduction channel are additional components that add weight and, therefore, may reduce fuel efficiency. This patent also fails to disclose any method of reducing unwanted detonations as temperatures in the firing cylinders increase.
These and other problems and disadvantages associated with prior art camless engines and variable displacement engines are addressed by Applicants"" invention as summarized below.
According to the present invention, a variable displacement internal combustion engine is disclosed that has a plurality of internal combustion cylinders that are operable in a firing mode or in a compressor mode. The engine has an intake manifold that provides air to a first set of intake valves provided for each of the cylinders. A boost manifold receives compressed air from non-firing cylinders operating in the compressor mode and provides compressed air to cylinders operating in the firing mode. Each cylinder has an intake valve controlled by an electromagnetic actuator, an intake/compressed air valve controlled by a second electromagnetic actuator, and an exhaust valve controlled by another valve actuator. The intake/compressed air valves of cylinders operating in the compressor mode are timed to selectively provide compressed air to the boosted manifold when vehicle operation requires additional torque.
According to one embodiment of the invention, a subset of cylinders are ported to the boost manifold and may be selectively operable in the compressor mode. Alternatively, all of the cylinders of the engine may be selectively operable in the compressor mode wherein all of the cylinders would be ported to the boost manifold.
According to another aspect of the invention, the engine may be a four-cycle engine having an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. The four-cycle engine may be operated in a full cylinder mode wherein the intake valves and intake/compressed air valves open during the intake stroke and the exhaust valve opens during the exhaust stroke.
A further aspect of the invention is that it is a four-cycle engine (as described above) that may be operated in a variable displacement mode. In the variable displacement mode, the intake valves open during the intake stroke and the combustion stroke, the intake/compressed air valves open during the compression stroke, and the exhaust valve opens during the exhaust stroke.
According to yet another aspect of the invention, the four-cycle engine (as described above) may be operated in a boosted variable displacement mode wherein the intake valves and intake/compressed air valves open during the intake stroke, the intake valves close during the compression stroke, while the intake/compressed air valves of non-firing cylinders open during the compression stroke and the exhaust valve opens during the exhaust stroke.
According to another aspect of the invention, exhaust gas from the firing cylinders may be introduced into the non-firing boosting cylinders by opening of the normally deactivated exhaust valves during a portion of the downward stroke. This recirculated exhaust gas is then delivered to the boosted manifold in order to reduce emissions.
It is an objective of the invention to use the non-firing cylinders of a variable displacement engine equipped with hydraulic or electromechanical valves to supercharge or boost the manifold pressure of the active firing cylinders and thereby increase the power output of the engine. The performance and efficiency of the firing cylinders and the non-firing cylinders that act as a two-stroke reciprocating compressor may be improved by utilizing adjustable valve timing. It is expected that a 30%-40% increase in torque may be achieved by the invention as compared to naturally aspirated variable displacement engines.
Another object of the invention is to reduce detonation, or spark knocks, by periodically using each of the cylinders when operated in the VDE mode as a compressor to reduce temperatures within the firing cylinders.
Another object of the invention is to improve fuel evaporation during startup and reduce feed gas hydrocarbon emissions by preheating the intake air of the firing cylinders by compressing it in the non-firing cylinders.
Yet another object of the invention is to extend the operating range for the engine operating in the VDE mode. Engine performance is also improved by eliminating the sudden surge in power when additional engine cylinders are activated. Fuel economy is improved and emissions reduced by operating fewer firing cylinders in the VDE mode with boosted manifold absolute pressure (MAP) instead of operating all cylinders with a reduced MAP.
Another object of the invention is to provide more stable combustion as a result of the higher manifold pressure in the boosted cylinders that facilitates exhaust gas recirculation and reduces feed gas NOx emissions.
Yet another object of the invention is to permit the output of boosted cylinders to vary in accordance with torque requirements and dependent upon intake/compressed air valve timing. The timing of intake/compressed air valves is optimized to efficiently deliver boosted charge with minimum parasitic losses.
It is yet another object of the invention to permit sequential intake valve timing of the intake valves relative to the intake/compressed air valves in each cylinder to promote the swirl of intake gases in the cylinder.
These and other objects and advantages of the invention will be readily apparent to one of ordinary skill in the art to which the invention relates.